Binding of factor VIIa to the endothelial cell protein C receptor reduces its coagulant activity

Abstract

Summary. Background: Endothelial cell protein C receptor (EPCR) binds protein C through its c-carboxyglutamic acid (Gla) domain and enhances its thrombin-thrombomodulin complex-dependent activation. So far, only protein C/ activated protein C has been shown to interact with EPCR. Factor VII (FVII), the coagulation trigger upon tissue factor (TF) interaction, is a serine protease whose Gla domain is highly homologous to the Gla domain of protein C. Objectives: To characterize the binding of FVII/FVIIa to EPCR and its functional consequences. Methods and results:We demonstrated by surface plasmon resonance (SPR) that FVII/FVIIa binds to EPCR through its Gla domain. At therapeutic concentrations, FVIIa reduced the activation of protein C by 40%. Soluble EPCR (sEPCR) was also able to prolong dose-dependently the clotting time induced by the FVIIa-TF complex. SPR and amidolytic experiments showed that FVIIa is able to interact simultaneously with TF and EPCR, thus ruling out the possibility that the effect of EPCR on clotting time was due to the inhibition of the binding between FVIIa and TF. sEPCR inhibited dose-dependently the activation of FX by the FVIIa-TF complex. Notably, blocking the binding site of EPCR on the endothelial surface increased the generation of FXa 2-fold. Conclusions: EPCR binds to FVII/ FVIIa and inhibits the procoagulant activity of the FVIIa-TF complex.

Factor VIIa binding to endothelial cell protein C receptor

“…This suggests that EPCR does not induce the necessary essential allosteric conformational changes in FVIIa to enhance its proteolytic activity [3]. However, Lopez-Sagaseta et al [17] reported a noticeable influence of sEPCR on the amidolytic activity of FVIIa, suggesting that the molecule does undergo a structural rearrangement involving its active site. It is interesting to note that sEPCR increased the amidolytic activity of FVIIa even when FVIIa was complexed with TF [17].…”

“…Thus the binding of FVIIa to EPCR will not have a significant influence on the formation of TF:FVIIa complexes on activated endothelial cells. In light of this, a recent observation that showed blocking of the EPCR binding site on EA.hy926 cells increased the generation of FXa at low concentrations of FVIIa [17] is surprising. However, we are unable to reproduce these data with stimulated HUVEC (unpublished data).…”

“…Protein C binding to EPCR is mediated by the Leu-8 residue in the ω-loop of the Gla domain [15], and this binding region is completely conserved in FVII. An alanine mutant scanning approach with EPCR showed that the residues of EPCR previously identified as being directly involved in the interaction with protein C/APC [16] are also involved in the binding of FVII/FVIIa [17].…”

“…However, Lopez-Sagaseta et al [17] reported a noticeable influence of sEPCR on the amidolytic activity of FVIIa, suggesting that the molecule does undergo a structural rearrangement involving its active site. It is interesting to note that sEPCR increased the amidolytic activity of FVIIa even when FVIIa was complexed with TF [17]. These data need to be confirmed.…”

Factor VIIa Interaction With Tissue Factor and Endothelial Cell Protein C Receptor on Cell Surfaces

“…FVIIa binding to EPCR has no influence on the formation of TF-FVIIa complexes on activated endothelial cells (31). However, Lopez-Sagaseta et al (37) recently reported that soluble EPCR dose-dependently inhibited TF-FVIIa activation of FX. They also showed that blocking the EPCR binding site on the endothelial cell surface increased the generation of FXa.…”